What's with the 3Gb memory barrier?
 

Yes, if you install 8Gb of RAM (the artificially-limited maximum for Vista Home Basic; Home Premium can take 16Gb) in 64-bit Vista, you'll be able to use more than 7Gb of that RAM, no matter what. But unless you're using 64-bit workstation/server applications (not just Photoshop), or multitasking a whole lot of big 32-bit apps, the extra memory will only give you a small performance gain. Small enough that if someone steals half of your memory, you may well not notice.

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